Unless all your races are going to take place in tropical waters, such as in Hawaii, then a wetsuit is an essential piece of race equipment. This holds true whether you come from a competitive swimming background or not.
Free speed is the most significant performance benefit of a wetsuit. Wetsuit buoyancy improves your body position so you "ride" higher in the water. This translates into less resistance, which directly correlates with faster times.
This advantage is certainly greater for less experienced swimmers than for experienced ones that already have good body position. Still, the advantage is real.
Better insulation against frigid water temps is another benefit. Wetsuits make more races possible, particularly the longer ones. The danger of extended exposure to cold water would be just too great for these events to take place without the added warmth of a wetsuit.
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The third benefit is safety. While your wetsuit is not a flotation device, it will keep you on top of the water in case you need to swim to the side, roll over on your back and stop for a moment to collect yourself.
If you want to see how this works, take your wetsuit out for a test ride and try swimming under water. You won't be under very long before you pop back up to the surface like perfectly cooked ravioli.
How to Choose a Wetsuit
There are lots of wetsuits to choose from so ask yourself some questions first to think through your needs.
What's your goal?
Is triathlon a bucket list item you'll be done with after a race or two? Do you see triathlon as a lifestyle that you're in for the long haul? Do you plan to race frequently or just enough to justify your passion? Take some time to noodle on this because if you don't plan on racing much or you're not sure, renting or borrowing a wetsuit may be the better option for you.
What's your budget?
Most wetsuit companies have entry level, mid-range and high-end offerings that range in price from $200 to $800 or more. The key benefit to the more expensive suits is that they're made of more flexible material that gives you improved range of motion during your swim.
For competitive triathletes and experienced swimmers, better flexibility is often a deciding factor. The bottom line here is that it's a relatively expensive piece of gear that you might not use very often.
What's the right sleeve length?
If you do decide to buy then a long-sleeve suit is probably best. A full suit is slightly faster because the extra material makes you more buoyant and it will give you that little extra warmth.